The invention relates to a guide tube for a portable handheld work apparatus such as a brushcutter, hedge trimmer or the like. The work apparatus has a drive motor mounted on one end of the guide tube and a tool mounted at the other end thereof. The tool is fixedly attached to the guide tube via a flange of a gear case. The tool is driven by a drive shaft disposed in the guide tube.
Guide tubes or protective tubes of the above kind are used with portable handheld work apparatus such as brushcutters, hedge trimmers or the like, wherein a drive motor is mounted at a spacing to a driven tool. The drive motor is attached to one end of the guide tube and guides a work tool mounted at the other end of the guide tube via a drive shaft running in the guide tube. The work tool is connected via a gear case and can be a filament cutter, a knife or also a hedge cutter blade. The gear case is provided with a flange configured as a receptacle bushing or the like wherein the end of the guide tube facing toward the flange is inserted over a partial length thereof and held. Stress peaks can occur in the guide tube at the transition of the attachment flange to the guide tube during operation of the work apparatus such as a brushcutter, overhead branch cutter, hedge trimmer or the like. These stress peaks have to be taken up with a corresponding configuration and dimensioning of the guide tube.
It is an object of the invention to provide a guide tube which is improved so that force is introduced into the guide tube in a simple manner.
The guide tube assembly of the invention is for a portable handheld work apparatus including a brushcutter, hedge trimmer or the like. The work apparatus has a drive motor and a work tool and the guide tube assembly includes: a guide tube having a first end on which the drive motor is mounted; the guide tube having a second end; a gear case connected to the work tool; the gear case having a flange mounted on the second end of the guide tube; a drive shaft rotatably journalled in the guide tube for operatively connecting the drive motor to the work tool to permit the work tool to be driven by the drive motor; a reinforcing sleeve inserted into the guide tube at the second end thereof; and, the reinforcing sleeve projecting axially along a part length (Lxe2x80x2) of the guide tube out from the end of the flange into the guide tube in the assembled state of the gear case.
In the guide tube of the invention, a reinforcing sleeve is inserted at least into the work tool end of the guide tube in the attachment segment. The reinforcing sleeve can be configured longer than the attachment segment and projects axially from the work tool flange along a part length of the guide tube. The reinforcing sleeve reinforces the guide tube especially in the transition region to the attachment segment. During operation, changing loads and vibrations occur especially in work tools such as a hedge trimmer blade, a knife or a running saw chain with these loads and vibrations being introduced into the guide tube. A step-like cross-sectional jump at the inner diameter of the guide tube is achieved in an axial direction toward the work tool by the reinforcing sleeve pushed axially into the guide tube. In the guide tube, stress peaks are avoided in the region of the force-introducing work tool flange.
Preferably, the reinforcing sleeve has a slot over its length which preferably conically expands at one end of the reinforcing sleeve. With this constructive measure, it is possible to insert a reinforcing sleeve into a longitudinally welded guide tube having an inner unmachined weld seam. The conical expansion of the slot with beveled edges effects a centering of the slot on the weld seam so that the insertion is facilitated. It is practical to configure the clear width of the slot wider than the weld seam. Preferably, the width of the slot is approximately one quarter of the diameter of the reinforcing sleeve in order to make possible a rapid mounting without jamming of the reinforcing sleeve in the guide tube.
At one axial end of the reinforcing sleeve, a radial stop projects outwardly and is provided as an axial stop of the reinforcing sleeve against the guide tube. The stop can be provided as a bent-over collar or lug. The collar or several lugs are arranged on the axial end opposite the conical widening of the slot.
It is practical to configure the reinforcing sleeve as a steel sleeve or to manufacture the reinforcing sleeve from longitudinally welded sheet metal.
The diameter of the reinforcing sleeve is selected approximately equal to or preferably slightly greater than the inner diameter of the guide tube. With these constructive measures, the reinforcing sleeve lies in the guide tube under radial tension. The reinforcing sleeve is elastically bendable especially because of the longitudinal slot therein and an elastic connection of guide tube and reinforcing sleeve is achieved in the flange region of the work tool. Peak stresses in the flange region of a work tool head are reliably conducted into the guide tube in this way.